Hi
I wanted to explain
| semaphore p1 p2 |
semaphore := Semaphore new.
p1 := [ semaphore wait.
'p1' crTrace ] fork.
p2 := [semaphore signal.
'p2' crTrace ] fork.
displays p2 and p1.
but I would like explain clearly but it depends on the semantics of signal.
- ==p1== is scheduled and its execution starts to wait on the semaphore, so it
is removed from the run queue of the scheduler and added to the waiting list of
the semaphore.
- ==p2== is scheduled and it signals the semaphore. The semaphore takes the
first waiting process (==p1==) and reschedule it by adding it to the end of the
suspended lists.
Now this sentence "The semaphore takes the first waiting process (==p1==) and
reschedule it by adding it to the end of the suspended lists.” is super naive.
Is the semaphore signalling scheduled? or not?
signal
"Primitive. Send a signal through the receiver. If one or more
processes
have been suspended trying to receive a signal, allow the first one to
proceed. If no process is waiting, remember the excess signal.
Essential.
See Object documentation whatIsAPrimitive."
<primitive: 85>
self primitiveFailed
"self isEmpty
ifTrue: [excessSignals := excessSignals+1]
ifFalse: [Processor resume: self removeFirstLink]"
I wanted to know what is really happening when a semaphore is signalled.
Now resume: does not exist on Processor.
I will look in the VM code.
S
S.
